I've spoken to Nerussa, the publican at the Wawnet Inn just outside the Imperial City. She's searching for a rare wine named Shadowbanish Wine that she says is most commonly found in fort ruins. She tells me if I retrieve six bottles, I'll be well compensated. Looks like I'll need to keep a careful eye out.

Update: Upon finding a bottle of Shadowbanish Wine, prior to speaking with Nerussa:

I've come across a bottle of wine with markings I've never seen before. I can barely make out "Shadowbanish Wine" on the label. It must be quite valuable. I should hold onto it until I find out more.

Update: Once the required number of bottles have been found:

I've recovered six bottles of Shadowbanish Wine. I should bring them back to Nerussa at the Wawnet Inn for my final reward.

Update: After talking to Nerussa:

I've given six bottles of Shadowbanish Wine to Nerussa. In return, she paid me a large finder's fee of 1000 gold. She also told me if I find any more bottles of the wine, she'd gladly pay me 100 gold each for them.